Pervasive Threat to Coral: Resilient Predator Thrives Amid Bleaching and Consumes Recovering Reefs

Pervasive Threat to Coral: Resilient Predator Thrives Amid Bleaching and Consumes Recovering Reefs

Image Caption: Young crown-of-thorns starfish observed alongside coral. Attribution: Monique Webb, Byrne, and team.

The crown-of-thorns starfish is an exceptional predator of coral, highly adapted to the changing thermal conditions of oceanic environments.

A study led by marine scientists at the University of Sydney has determined that young crown-of-thorns starfish are remarkably resistant to heatwaves, far beyond temperatures that prove fatal to coral. Once these juvenile starfish mature, they become predators that voraciously consume coral reefs during their recovery phase.

Notable Predator of the Great Barrier Reef

Endemic to the Great Barrier Reef and present in the Indo-Pacific zone, the crown-of-thorns starfish is identified as a species warranting concern. The destruction it wreaks on coral populations is unparalleled, second only to cyclones and bleaching incidents in terms of the negative impact on coral longevity.

Emerging research indicates that this species’ hardiness in warmer waters could amplify the devastating consequences of climate change on coral reef systems.

Study Overview and Conclusions

The findings were released on October 18 in the scientific journal Global Change Biology. The research was spearheaded by Professor Maria Byrne, who is affiliated with the School of Life and Environmental Sciences, the Marine Science Institute, and the Sydney Environment Institute.

Over the duration of the study, the heat tolerance exhibited by juvenile crown-of-thorns starfish was notably elevated, even when compared to their adult versions. This suggests that even if the predatory adults experience a decline due to climate-induced ocean warming, the herbivorous juveniles can bide their time until they mature into carnivorous predators.

Ramifications for Coral Biomes

When ocean temperatures rise by 1-3 degrees Celsius (1.8-5.4 degrees Fahrenheit) above typical summer highs, depending on the duration, it can instigate coral bleaching and subsequent death.

“Juvenile crown-of-thorns starfish can withstand nearly triple the thermal stress that results in coral bleaching, based on a model that accounts for temperature over a span of time,” stated Professor Byrne.

The professor further elaborated, “This is a critical discovery for comprehending the repercussions of climate change on marine ecosystems, particularly regarding the role of often-overlooked small cryptic species.”

“As waters warm, juveniles are likely to benefit. The increment in their rubble habitat, engendered by coral death and bleaching, enables their numbers to accumulate over the long term.”

Life Cycle and Contributing Factors

The crown-of-thorns starfish, a formidable predator of coral, displays a life cycle finely tuned to warmer oceanic conditions. During periods when their adult form is active, these starfish consume coral extensively, reducing them to barren skeletons that ultimately disintegrate. Coral mortality due to bleaching has a comparable effect.

The detritus of dead coral offers an ideal breeding ground for the starfish’s algae-consuming offspring. Earlier research by Professor Byrne shows that these juveniles can endure and remain dormant for at least six years, awaiting coral recovery. Once the reef revives, these juveniles metamorphose into coral-consuming predators, reinstating the vicious cycle.

Matt Clements, a PhD student and co-researcher, commented, “The juveniles’ heat resilience and their gradual population increase in the coral rubble over the years may significantly contribute to the onset of adult outbreaks of the crown-of-thorns starfish.”

Factors like overfishing and nutrient accumulation, previously implicated in such outbreaks, now share the stage with evidence that bleaching-induced coral death benefits the juvenile starfish, exacerbating climate change’s destructive effects on reefs.

The study also delineated contributing factors to the juveniles’ survival in warmer conditions, such as their small size reducing physiological needs, and their dietary flexibility, despite a preference for coralline algae.

Reference: “Juvenile waiting stage crown-of-thorns sea stars are resilient in heatwave conditions that bleach and kill corals” by Maria Byrne, Dione J. Deaker, Mitchell Gibbs, Paulina Selvakumaraswamy and Matthew Clements, published on 18 October 2023 in Global Change Biology.
DOI: 10.1111/gcb.16946

Frequently Asked Questions (FAQs) about crown-of-thorns starfish

More about crown-of-thorns starfish

• University of Sydney’s Marine Science Institute
• Global Change Biology Journal
• Great Barrier Reef Marine Park Authority: Crown-of-Thorns Starfish
• Impacts of Climate Change on Coral Reefs
• Coral Bleaching and Climate Change
• Sydney Environment Institute
• DOI for the Published Research